C51 or C-51 may refer to:
Legislation Anti-terrorism Act, 2015, introduced as Bill C-51 in the 41st Canadian Parliament, 2nd Session Bill C-51 of the 39th Canadian Parliament, 2nd Session, a proposed amendment to the Food and Drugs Act
Vehicles , an Admirable-class minesweeper of the Mexican Navy Caudron C.51, a French biplane floatplane Douglas C-51, an American transport aircraft JNR Class C51, a Japanese steam locomotive
Other uses Caldwell 51, an irregular dwarf galaxy Evans Gambit, a chess opening GeForce 6100, a graphics processing unit